The present invention relates to the fabrication of optical media with preformatted guide tracks for multi-track optical recording.
The high capacity of optical recording media is achieved by encoding data in very narrow data tracks, typically about 1 xcexcm wide. A tracking servo system is required to position the tracks so close together without overlap. The tracking servo system functions by sensing guide tracks that are preformatted on the optical recording medium.
The recording data rate of an optical recording system can be greatly increased by multi-track recording, whereby a band of data tracks are recorded simultaneously by a single optical head. The relative positions and parallelism of the tracks within the band are held fixed by optical alignment of recording sources within the head. However, a guide track is still required for each band of data tracks so that the tracking servo system can position data bands close together without overlap.
Existing methods for preformatting optical media are suitable to format optical disk media for single-track recording. However, these preformatting methods are slow and expensive, sometimes dominating the total cost of media manufacturing. Furthermore, these methods are not readily adaptable to create guide track formats for multi-track optical recording.
It is therefore an object of the present invention to provide a method for flexible, high speed preformatting of optical media for multi-track optical recording and to reduce the cost of optical media fabrication by reducing the complexity of the media preformatting process.
This object is achieved by a method for preformatting an optical recording medium with a plurality of parallel guide tracks, each guide track controlling the recording of a band of data tracks, said method comprising:
a) providing a source laser beam along a predetermined path at a wavelength which is selected to be within the sensitivity range of the optical recording medium;
b) providing a beam splitter in the predetermined path which divides the source laser beam into a multiplicity of preformatted recorded beams directed to impinge upon the optical recording medium, the spacing or pitch between the beams at the optical recording medium being uniform as viewed from a scan direction, such pitch being greater than at least three times the spacing between the data tracks after they are recorded;
c) simultaneously focusing the preformatted recording beams at a focal surface to form an array of focused spots;
d) positioning the optical recording medium with its recording surface at the focal surface; and
e) providing relative motion between the optical recording medium and the focused spots in the scan direction to form visible guide tracks in a recording zone of the optical medium that trace out the path of each focused spot.
The present invention has as an advantage that a precise guide track format for multi-track optical recording is formed at a high rate and at low cost. The invention also improves system performance in that reduced guide track runout leads to improved tracking accuracy and increased media capacity.
It is a further advantage of the present invention that it simplifies media manufacturing by allowing high-speed servowriting of the preformat pattern, thereby eliminating the need for specialized surface replication equipment and complex media structures. Servowriting imposes no additional constraints on the media design because it is a laser-marking process similar to data recording. Simplification of the servowriter system is achieved according to the present invention by writing a plurality of guide tracks with a single modulated laser beam.